Composites for sound control applications

ABSTRACT

A sound attenuating material includes a matrix, and a nanofiller, the material effectively reduces the level of low frequency sound incident thereon.

FIELD

Certain embodiments relate to composite materials comprising nanofillers, the composites being suitable for sound attenuation.

BACKGROUND

In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.

Sound energy is ‘absorbed’ when it is converted to another form of energy. In most cases, this takes the form of conversion to heat. This results from the actions of friction and the resistance of various materials to movement and deformation. Industries use porous absorbers for passive noise control. Porous absorbers such as mineral wool, fiberboard or plastic foams have an open pore structure. Conversion to heat is produced by friction when vibrating air molecules are forced through the pores and interact with the pore walls. These materials are effective primarily for high frequencies with short wavelengths. In a sound wave which is incident on a rigid wall, the maximum particle velocities occur at ¼ and ¾ of the wavelength. If the thickness of the absorber is less than one quarter of the wavelength, it has little effect.

Sound moves forward in a straight line when traveling through a medium having uniform density. However, sound is subject to refraction, the bending of waves from their original path. When a sound wave enters a denser medium, it will bend toward the denser medium. Conversely, when entering a less dense medium it will bend away. The speed of a wave depends on the elastic and inertia properties of the medium through which it travels. When a wave encounters a different medium where the wave speed is different, the wave will change directions. Most often refreaction is encountered in the study of optics, with a ray of light incident upon a boundary between two media (e.g., air and glass, air and water, or glass and water). Snell's law relates the directions of the wave before and after it crosses the boundary between the two media. As the wave fronts cross the boundary the wavelength changes, but the frequency remains constant. Sound waves, unlike light waves, travel faster in denser materials, such as solids and liquids, than they travel in air. When sound waves enter a solid, their velocity and wavelength increase and they are bent away from the normal to the surface of the solid.

The reflection of sound follows the law that the angle of incidence equals angle of reflection, sometimes called the law of reflection. The reflected waves can interfere with incident waves, producing patterns of constructive and destructive interference.

Sound waves reflect from boundaries between dissimilar materials. Changes in grain structure, fiber orientation, porosity, particle concentration, and other microstructural variations can affect the amplitude, direction, and frequency content of scattered signals. Scatter effects can also be monitored indirectly by looking at changes in the amplitude of a back wall echo or a through-transmission signal.

Sound travels through a pressure wave transport mechanism. This pressure is related to the speed of sound waveform. From linear wave theory we have equation (1):

$\begin{matrix} {{\nabla^{2}p} = {\frac{1}{c^{2}}\frac{\partial^{2}p}{\partial t^{2}}}} & (1) \end{matrix}$

Where c is defined as speed of sound. This parameter has a value of 340 m/s in air at ambient temperature. The speed of sound in solids is defined by equation (2):

$\begin{matrix} {c = \sqrt{\frac{\kappa}{\rho}}} & (2) \end{matrix}$

Where κ is the modulus and ρ is the density of the media that sound travels within. Equation (2) basically defines the characteristic that less stiff and heavier materials are better absorber materials because they reduce the speed of sound. If we assume that we have first and second regions between the sound barrier material, then we can calculate the amount of pressure difference needed to reduce the sound level.

In order to calculate the pressure gradient across the sound barrier, start with sound level definition by equation (3):

$\begin{matrix} {L_{p}^{1} = {20{\log_{10}\left( \frac{p_{1}}{p_{0}} \right)}}} & (3) \end{matrix}$

In the equation above the sound pressure at point 1 is related to sound pressure level in decibel (dB) through a reference pressure which is defined by equation (4):

p ₀=20×10⁻⁶ Pa (20 μPa)  (4)

Defining the sound pressure level at point 2 using equation (5):

$\begin{matrix} {L_{p}^{2} = {20{\log_{10}\left( \frac{p_{2}}{p_{0}} \right)}}} & (5) \end{matrix}$

Equations (3) and (5) can be simplified to obtain equation (6):

$\begin{matrix} {{\Delta \; p} = {{p_{2} - p_{1}} = {p_{0}10^{(\frac{L_{p}^{2}}{L_{p}^{1}})}}}} & (6) \end{matrix}$

As an example, to reduce sound level from 140 dB (harmful to ears) to 30 dB (pleasant) the pressure difference should be 32 μPa.

Passive control of noise utilizing specialized materials for sound isolation, sound absorption and vibration damping has played a major role in improving our environment, at home and in the workplace, for over fifty years. The theory on which the technology is based has also existed for quite some time. Modern technology has continually advanced the variety of commercially available noise and vibration control materials. Sound absorption materials, for example, range from mineral wool and glass fiber blankets to open cell foams made of polyurethane, polyimide and melamine, having a variety of surface treatments. Lead-free, mass loaded vinyl is frequently used as a limp mass element in sound barrier materials, which can be combined with foam layers to add sound absorption and create decoupling between several noise barrier layers. The effectiveness of all these materials as sound absorbers or isolators is highly frequency dependent.

Traditional passive noise control materials fail to adequately achieve sound attenuation over the complete frequency range of, for example, 125 Hz to 8000 Hz. In order to reduce noise level at low frequencies, the thickness of conventional sound control materials is increased. However, increasing thickness increases weight, cost, and complexity of usage. Moreover, at least some traditional passive noise control materials in the form of composites comprising a matrix and a filler material are typically characterized by large amounts of filler. Such composites which include relatively large amounts of filler often lack desired physical properties due to degradation of the properties of the composite caused by excessively large amounts of filler contained in the matrix thereof.

SUMMARY

The present invention addresses one or more of the above-mentioned disadvantages associated with the state-of-the-art.

Described herein are composite materials which reduce sound levels over a wide range of frequencies by utilizing relatively low amounts of nanometer sized filler materials dispersed within a matrix without resorting to significant increases in thickness of the composite material. In some embodiments, the composite material comprises a polymer and a nanofiller.

The nanofiller may be dispersed in the matrix of the composite. According to a first aspect, the present invention provides sound attenuating material comprising: a matrix; a nanofiller having an average size of about 1 nm to about 50 μm; the material comprising 0.1-30.0 wt. % nanofiller, and wherein the material reduces the level of sound having frequency ranges of up to about 1,000 Hz by at least about 5 dB.

According to further aspects, the present invention provides sound barriers and/or sound emitting devices comprising the above-described sound attenuating material.

As used herein, the term “nanofiller” means a substance or substances that are characterizable by an average particle size of about 1 nm to about 1,000 nm. The term nanofiller is not geometry-specific, thus the nanofiller's size characteristic refers to at least one dimensional measurement thereof. The term nanofiller, as used herein, is also not specific to composition. Thus, nanofiller may comprise elemental substances as well as compounds, polymers, and the like.

As used herein “average particle size” or “average size” refers to the fact that there is particle-to-particle variation in the size measurement of particulate-type materials. In other words, not all of the nanofiller particles may be of the same size, or even the same geometry. The particle size of the nanofiller as referenced herein can be measured and obtained by any suitable method familiar to those skilled in the art, such as SEM, AFM, STM, Dynamic Light Scattering, Disc Centrifuge, Laser Diffraction, and Acoustic Spectroscopy for nano- and micron-size particles. Some other techniques such as Microscopy, Sedimentation, and Electrozone Sensing may be used for micron-sized particles. Typically, a representative number of particle size measurements are taken, resulting in a distribution of size measurements. An average or other statistical representation of the distribution is then determined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a composite material and sound barrier formed according to the principles of the present invention.

FIG. 2 is a cross sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a schematic illustration of a sound-emitting device including one or more the sound barriers comprising a composite material constructed according to the principles of the present invention.

DETAILED DESCRIPTION

According to the present invention, composite materials which reduce sound levels at a wide range of frequencies can include a matrix and one or more nanofillers.

The particular matrix material which can be used in the composite materials of the present invention is not particularly limiting and may include polymers and polymeric resins, aerogels, nonwoven fibrous materials, or combinations of the foregoing.

Suitable polymers and polymeric resins may include those polymers currently used for sound absorption applications such as open celled foamed polymers. For example, polyurethane, polyimides, polycyanurates, polyesters and melamine may be used as the polymer in the composite material.

Other suitable polymer and polymeric resins include, but are not limited to, polystyrene, polyurethane, polyolefins such as polyethylene or polypropylene, hydrogels, polyacrylates, polyarylenes, polycarbonates, polyureas, polycyanurates, polysulfones, epoxies, nylons, aramids, polyvinyl chloride, polymers of (meth)acrylic acid or the esters and/or salts of (meth)acrylic acid, polyesters, rubber, PTFE, silicone, and mixtures of two or more of any of the foregoing. The polymer may also be a polymer of one or more of the monomers comprising the polymers of the foregoing. For example, the polymer may be a copolymer of styrene and acrylonitrile.

Another polymer medium that can be used is hydrogel. Hydrogel is a network of polymer chains that are water-soluble, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels can be created in many ways, and is not limited to any one particular method of formation. For example, the hydrogels may be made of one or more materials selected from the group consisting of polyvinyl alcohol, sodium polyacrylate, (meth)acrylate polymer, and other polymers with an abundance of hydrophilic groups. Preferred hydrogels include 2-hydroxyethylmethacrylate (HEMA) hydrogels, but are not limited thereto. Another suitable hydrogel material includes N-vinyl-pyrrolidone (NVP).

In some embodiments, cross linkers may also be used in the polymers. For example, ethylene glycol dimethacrylate (EDGMA) may be used. Another nonlimiting example of a cross linker is polyethylene glycol dimethacrylate (PEDGMA).

In some embodiments of the polymer composite materials, a photoinitiator is required. For example, 2,2-dimethoxy-2-phenyl acetophenone may be used as a photoinitiator. In some embodiments, the photoinitiator may help assist in the reaction of the polymerization and/or curing of the polymers. For example, UV irradiation of a polymer comprising 2,2-dimethoxy-2-phenyl acetophenone results in the curing of the polymer composite material.

It is also contemplated but the present invention that the composite materials can comprise combinations of materials present in one or more layers. For example, a composite material constructed according to the principles of the present invention may comprise one or more layers of nonwoven fibrous sheets layered together, and possibly with layers of other materials, as a multiple-layered laminate-type composite. Alternatively, the nonwoven fibrous sheet, optionally combined with other materials, may be presented as a single-layered construction.

Nanofillers may be dispersed in a matrix of the polymer or polymeric resin. In some embodiments, nanotubes may be dispersed in the polymer matrix. The nanotubes may be based on carbon and/or other elements. In some embodiments, the nanotubes are cylindrical and comprise a hexagonal lattice of carbon and/or other elements. In some embodiments, the nanotubes are metallic and/or semiconductive. In some embodiments, the nanotubes exhibit a high tensile strength. In one embodiment, single walled nanotubes may be used. In other embodiments, multi-walled carbon nanotubes are used.

In some embodiments, nanofillers, as described herein, are substantially uniformly dispersed in the matrix. Substantially uniform dispersion within the matrix may improve the ability of the composite material to attenuate sounds which are incident to the composite. In some embodiments, the nanofillers may be physically dispersed using a mechanical device. For example, in some embodiments, the nanofillers and matrix material may be mixed in a mixer or extruder to achieve a substantially uniform dispersion.

In some embodiments, the nanofillers are modified. In some embodiments, the nanoparticles are modified by inclusion of an organic functional group on the nanofiller. In some embodiments, a benzyl group is a used as a organic functional group. Other organic functional groups include hydroxyl, acetyl, phenyl, alkyoxy, alkyl (e.g., methyl, ethyl, propyl, and substituted alkyls). In another embodiment, inorganic salts may be added to the composite to change the hydrophobicity of the composite. In some embodiments, the nanotubes are modified with NaOH. In some embodiments, the modification of the nanofillers provides a more hydrophobic composite material. Additionally, such modification may result in substantially more uniform dispersion of the nanofiller within the matrix of the composite material than compared to a composite without the modification. In some embodiments, the metal (oxide) nanoparticles are modified to increase the interaction of the polymer and nanoparticles. However, the composite materials as disclosed herein are not limited to modified nanofiller materials.

Nanofillers may also include metal or metal oxide nanoparticles. In some embodiments, the metal or metal oxide nanoparticles are colloidal. Some exemplary nanoparticles include silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), tin oxide (SnO₂), iron oxide (Fe₂O₃), zinc oxide (ZnO), magnesium oxide (MgO), zirconium oxide (ZrO₂), cerium oxide (CeO₂), lithium oxide (Li₂O), and silver oxide (AgO). The colloidal metal (oxide) nanoparticles may also include, but are not limited to, one or more metals such as silver (Ag), nickel (Ni), magnesium (Mg), and zinc (Zn). In some embodiments, one or more metal and/or metal oxides nanoparticles are used in combination. In some embodiments, mixed metal oxide nanoparticles may also be used.

Other nanofillers include a nanoclay material called montmorillonite—a layered smectite clay. Clays, may also be modified to be more “organic” to interact successfully with polymers. One way to modify clay is by exchanging organic ammonium cations for inorganic cations from the clay's surface.

Additional nanofillers include graphite platelets, carbon nanofibers, synthetic clays, natural fibers (hemp or flax), barium sulfate and polyhedral oligomeric silsesquioxane (POSS).

In some embodiments, one or more metal alloy nanoparticles may be used. Such nanoparticles include a metal alloy nanoparticle comprising one or more metals selected from aluminum (Al), copper (Cu), gold (Au), iron (Fe), nickel (Ni), platinum (Pt), silver (Ag), tantalum (Ta), tin (Sn), titanium (Ti), and zinc (Zn).

In some embodiments, the nanofillers may be one or more selected from nanopowders, nanotubes, nanofibers and nanoparticles. Some nanopowders include, but are not limited to, aluminum nitride, carbon, silicon, magnesium hydroxide, silicon carbide, silicon nitride, or titanium carbide. In some embodiments, oxide nanopowders may also be used. Such oxide nanopowders include, but are not limited to, one or more selected from aluminum oxide, silica, and titanium oxide.

Nanofillers described herein may be used in various sizes and shapes. In some embodiments, the nanofillers have an average size from about 1 nm to about 1,000 nm. In some embodiments, the nanofillers have an average size of about 10 nm to about 100 nm. In some embodiments, the nanofillers have an average size of about 30 nm to about 300 nm. In additional embodiments, the nanofillers have an average size of about 1 nm to about 50 nm. In one exemplary embodiment, the nanoparticles have an average size of about 100 nm. In some embodiments, the nanoparticles may have different average sizes, such as a bimodal or trimodal particle size distribution.

In certain embodiments, the nanofillers are used in amounts of up to 50 percent by weight of the total composite material. In a few embodiments, less than 1 weight percent of nanofiller may be used. In some embodiments, the nanofiller are about 0.3 to about 0.7 weight percent of the total composite material. In other embodiments, the nanofillers are about 0.1 to about 30 weight percent of the total composite material. In some embodiments, the nanofillers are about 0.1 to about 15 weight percent of the total composite material. In some embodiments, the nanofillers are about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.4, 9.6, 9.8, and 10 percent by weight based on the weight of the total composite material.

As will be understood by a person having ordinary skill in the art, the composite materials may be made according to many different methodologies. In some embodiments, monomers of a polymer matrix are mixed in a solvent or other suitable medium. The nanoparticles may beg added prior to, during, or after the polymerization process of the monomer units. In some embodiments, polymer may be added to a solvent or other suitable medium. In the foregoing embodiment, the nanoparticles may be present in the solvent when the polymer is added, or may be added to the solution or dispersion after the addition of the polymer. In some embodiments, a mixture comprising the nanoparticles and polymer may be sonicated.

In some embodiments, the composites are constructed by dispersing a nanofiller material into a matrix according to a pattern or concentration gradient. Non-homogenous dispersions of the nanoparticles in the matrix may form a “torturous path” for sounds: The dispersion of the nanofiller may also create a modulus differential, and a density between the matrix and the filler, which allows for the reduction of sound levels in certain embodiments.

FIGS. 1-2 are schematic illustrations of a composite material and sound barrier layer 10 constructed according to the principles of the present invention. The composite material of the present invention can take any suitable form. The form illustrated in FIGS. 1-2 is that of a relatively thin sheet or layer 10 having a thickness T. The thickness T can be on the order of tens of microns (e.g., 0.008 in or less) but could also be much thicker, based on the application. However, it should be understood that a composite material the present invention is clearly not limited to such geometries or forms. The composite material generally comprises a matrix 12 within which a nanofiller 14 is distributed therein. According to the illustrated embodiment, the nanofiller 14 is substantially uniformly distributed within the matrix 12. Again, the present invention is not so limited. For example, the nanofiller 14 may be non-uniformly distributed within the matrix 12 such as would be the case if the nanofiller was present in the form of a concentration gradient or other suitable distribution.

In an exemplary embodiment wherein the matrix is a polymer, after polymerization is complete, the composite material may be cast into a mold. In some embodiments, the polymer composite material may be molded into various shapes. In certain embodiments, the polymer composite material may be cast into the form of a wall, ceiling, or floor panels. Panels comprising the composite material as described herein may be used to control room acoustics. In other embodiments, the polymer composite may be shaped into an enclosure to block the sound of an audible device. For example, as illustrated in FIG. 3, the composite material may line 30 or enclose 40 a computer housing 20 to dampen the sounds from the computer parts (e.g., fan, motherboard, etc.). The polymer composite material may also be used to enclose one or more audible mechanical parts such as a compressor, engine, or pump.

According to a further embodiment, wherein the matrix is a polymer, after polymerization is complete the composite is reduced to solid pellets or granules. These pellets of granules can then be used to form various parts or components of the composite material by suitable techniques such as injection molding.

The composite materials of the present invention may reduce sound levels over a wide range of frequencies, but are especially interesting for their ability to reduce sound at lower frequencies such as 0.1 Hz to 1,000 Hz, 1 Hz-1,000 Hz, or 125 Hz-1,000 Hz. The composite materials can reduce sound levels by up to about 39 dB. In some embodiments, the composite materials reduce sound levels by up to about 34 dB. In some embodiments, the composite materials reduce sound levels at levels by about 0.5 to about 35 dB at a given frequency. In some embodiments, the composite materials reduce sound levels by about 2 to about 25 dB at a given frequency. In some embodiments, the polymer composite materials reduce sound levels by about 5 to about 20 dB at a given frequency. In some embodiments, the polymer composite materials reduce sound levels by about 10 to about 15 dB at a given frequency.

Composites formed according to the present invention may also effectively attenuate the sound level at frequencies above 1000 Hz to below the typical human ear threshold or to comfort levels.

The total frequency range over which the composite material may reduce sound levels ranges from about 15 to 20,000 Hz. In some embodiments, the composite materials reduce sound levels ranging in frequencies from about 0.1 to about 4,000 Hz. With certain embodiments, the composite materials reduce sound levels ranging in frequencies from about 0.1 to about 1,000 Hz.

Composite films formed according to the present invention in some cases are as thin as, for example, 0.008 in. thick. This does not restrict the thickness to less than 0.008 inch films. Sound level attenuation of close to 40 dB over a 0-16000 Hz frequency range (Octave model) using thin films of 0.008 inch has been achieved by experiment. By using thicker material even higher sound attenuation up to typical human ear comfort level, or even below the threshold, can be achieved.

Thickness requirements of the composite material of the present invention may be less than that of conventional passive sound control materials. For example, a composite material comprising 100 mg of multi-walled carbon nanotubes in a cast sheet having a thickness of 0.22 inches has the equivalent sound reduction as a conventional sound attenuating foam having a thickness of 0.5 inches. Thus, according to the foregoing example, the composite material requires, in some embodiments, less than half of the thickness required of a conventional foam sound absorption material.

Also, described herein are methods for reducing sound levels. One embodiment includes a method of reducing a sound level comprising providing a composite material, wherein the composite material comprises a polymer matrix and nanofillers. In certain embodiments, the nanofillers may be nanoparticles or nanotubes. In other embodiments the nanofiller may comprise silver particles, and the polymer matrix comprises polystyrene. In some embodiments of the foregoing methods, the polymer composite material is applied to an article to dampen sound that the article produces. In other embodiments, the polymer composite material is applied to an article to reduce the sound level of a sound that is incident on the article. In some embodiments, the polymer composite material may be cast into a shape prior to, during, or after application to an article.

Articles that are incident to sound waves may comprise the composite materials as described herein. The articles may contain the composite material on the surface of the article. However, the composite material may also be contained within the article and not on a surface. For example, building materials, such as wall panels, may comprise the composite material. The composite material may be placed on a surface of a wall panel, or it may be found within the wall panel. A preferred location for the composite material as described herein is a location such that sound waves are incident thereon.

Articles which produce sound or sound waves may also comprise the composite material as described herein. For example, a computer which produces sound may have a computer housing which comprises the composite material (e.g., FIG. 3). Thus, many enclosures that at least partially surround an article that produces sound may comprise the composite material as described herein.

Articles may also comprise one or more layers of the polymer composite material as described herein. More than one layer of the composite material may used to further reduce the sound levels at certain frequencies.

Different methods for mixing or dispersing the nanofillers within the matrix may be used. Without wishing to be bound to any particular theory, it is believed that one or more of uniform filler dispersion, difference in modulus, and the density difference between the matrix and the filler allows for the efficient reduction of sound levels.

The invention is further described in terms of the following examples which are intended for the purpose of illustration and not to be construed as in any way limiting the scope of the present invention, which is defined by the claims. In the following examples, all parts and percentage are by weight unless otherwise indicated.

EXAMPLES Experimental Setup

The experimental setup includes: a speaker as a noise source; a microphone as recording device, a personal computer for data acquisition; a sound level meter for calibration; analysis codes such as Matlab simulink and toolboxes; a sound isolation box; and samples of various sound control materials. The noise is created by the speaker and the amount of noise, after passing through the sound control media, is captured via the microphone. Real time acquisition and data analysis is performed through a computer. A sound level meter is used for calibration purposes. The meter is connected to the computer through an R232 port thereby enabling data acquisition in real time. The sound control material samples are formed as cylindrical cartridges or blanks. Different responses from different materials were recorded and analyzed using the computer.

Using Matlab and Simulink toolbox, initial testing started. Taking care to keep every other parameter the same, the sound control material was placed between the source and the microphone at a fixed distance from the speakers for all the performed tests.

Amplitude of the sound wave over time and the frequency response of the sound using Fast Fourier Transform (FFT) are monitored.

Material Preparation

Different nanofiller materials and concentrations were tried in combination with different matrix materials. Examples of such composites include:

1. Hydrogel-carbon nanotube composites. The following procedure was used to prepare hydrogel-nanotube composites:

Pour 9 g Hydroxy Ethyl Methacrylate (HEMA) and then add 6 g deinonized water;

Add 0.09 g of ethylene glycol dimethylate (EDGMA) to the above solution;

Shake the above solution for about 30 seconds;

Add 0.045 g 2,2 Dimethoxy-2 phenyl acetophenone (%99 pure) and mix the solution well for 1 minute;

Add 50 mg and 100 mg multiwalled nanotube fillers modified with NaOH or benzyl groups and perform stirring; and

Use ultraviolet light to cure the composite.

2. Polystyrene-carbon nanotube composites: Polystyrene as the matrix and carbon nanotubes as fillers.

Dissolve 1 g polystyrene beads in 10 ml of toluene while stirring;

Prepare modified multiwalled carbon nanotubes by mixing 3 mg and 6 mg of carbon nanotubes along with 5 ml NaOH to form a number of solutions;

Sonicate each solution for about 1 hour;

Remove the nanotubes from each solution by using a 0.2 micron PTFE filter;

Wash off the nanotubes from the filter in polystyrene and toluene solution using sonication for 10 minutes;

Remove the filter and sonicate the combination of polystyrene, toluene, and nanotubes for 3 hours; and

Cast the combination in a circular dish to create sound control composite cartridges or blanks.

3. Polystyrene-silver composites: Polystyrene as the matrix and modified silver nanoparticles as fillers.

Dissolve 1 g polystyrene beads in 10 ml of toluene while stirring;

Purchased modified silver nano particles and mix in various amounts (150 mg and 300 mg) in the polystyrene and toluene to form a number of different solutions;

Sonicate each solution for about 3 hours; and

Cast the polymer in the circular dish to create the sound control composite cartridges or blanks;

4. Polyester-silver-polystyrene composites: Polyester and silver nanoparticles composite prepared using a composite of polystyrene as the matrix and modified silver nanoparticles as fillers attached to thin layer of polyester film.

Dissolve 1 g polystyrene beads in 10 ml of toluene while stirring;

Purchased modified silver nanoparticles and mix in various amounts (150 mg and 300 mg) in the polystyrene and toluene to form a number of different solutions; Sonicate each solution for about 3 hours; and

Cast the polymer in the circular dish to create the sound control composite cartridges or blanks; and

Attach 0.002 and 0.004 inch polyester films to the casted composite.

The polystyrene film may be replaced by the polyester film.

Results

It should be noted that the lab “background” noise level is around 55 dB for the experiments.

The time domain response of various materials is easy to produce and is good for a general comparison, but for detailed analysis, frequency domain analysis is followed.

For the hydrogel composites, the effects of the addition of 50 and 100 mg of nanotubes to the hydrogel matrix was studied and compared relative to pure hydrogel. Comparisons between no sound barrier, commercial polyurethane foam, hydrogel-nanotube composites, and polystyrene-nanotube composites were also performed. In addition, the frequency responses of polystyrene-nanotube and polystyrene-silver nanofillers composites were also evaluated.

The results of the above comparisons confirm that the addition of nanofillers to the polymer matrix improves the sound control properties of the passive control media. This enhancement is varied over various frequency values but it has been shown that addition of even small amount of nanofiller in case of hydrogels and polystyrene matrix, will reduce the sound level at some lower frequencies (e.g., between 1 Hz and 1,000 Hz) somewhere between 5 to 15 dB.

TABLE I .22″ thick Hydrogel composite Properties Sound level [dB] No barrier 90 Hydrogel/50 mg CNT 74 Hydrogel/100 mg CNT 73

TABLE II 200 μm thick polystyrene and nanotube composite Properties Sound level [dB] No barrier 90 Polystyrene/3 mg CNT 58 Polystyrene/6 mg CNT 52

TABLE III 200 μm thick polystyrene and silver nano particles composite Properties Sound level [dB] No barrier 90 Polystyrene/150 mg Ag 56 Polystyrene/300 mg Ag 51

All numbers expressing quantities of ingredients, constituents, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about”. Notwithstanding that the numerical ranges and parameters setting forth, the broad scope of the subject matter presented herein are approximations, the numerical values set forth are indicated as precisely as possible. Any numerical value, however, may inherently contain certain errors as evident from the standard deviation found in their respective measurement techniques, or by rounding off.

Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims. 

1. A sound attenuating material comprising: a matrix; a nanofiller having an average size of about 1 nm to about 50 μm; the material comprising about 0.1-30.0 wt. % nanofiller, and wherein the material reduces the level of sound at low frequency ranges of up to about 1,000 Hz by at least about 5 dB.
 2. The material of claim 1, wherein the matrix comprises a polymer.
 3. The material of claim 2, wherein the polymer comprises: polystyrene, polyurethane, polyethylene, polypropylene, hydrogels, polyacrylates, polyarylenes, polycarbonates, polyureas, polycyanurates, epoxies, nylons, aramids, polyvinyl chloride, polymers of (meth) acrylic acid or the esters and/or salts of (meth) acrylic acid, polyesters, rubber, PTFE, silicone, mixtures of two or more of any of the foregoing, or copolymers comprising one or more of the monomers of the foregoing polymers.
 4. The material of claim 2, wherein the matrix comprises an open celled foam of polyurethane, polyimides, polycyanurates, or melamine.
 5. The material of claim 2, wherein the matrix comprises polystyrene.
 6. The material of claim 2, wherein the matrix comprises a hydrogel.
 7. The material of claim 6, wherein the hydrogel comprises polyvinyl alcohol, sodium polyacrylate, (meth)acrylate polymer, 2-hydroxyethylmethacrylate, or N-vinyl-pyrrolidone.
 8. The material of claim 1, further comprising a cross-linking agent.
 9. The material of claim 8, wherein a cross-linking agent comprises: ethylene glycol dimethacrylate or polyethylene glycol dimethacrylate.
 10. The material of claim 1, further comprising a photoinitiator, the photoinitiator comprises 2,2-dimethoxy-2-phenyl acetophenone.
 11. The material of claim 1, wherein the matrix comprises an aerogel.
 12. The material of claim 1, wherein the matrix comprises a nonwoven fibrous material.
 13. The material of claim 1, wherein the nanofiller comprises one or more of: nanopowders, nanotubes, nanofibers and nanoparticles.
 14. The material of claim 13, wherein the nanofiller comprises one or more of: carbon nanotubes, carbon nanopowders, graphite platelets, carbon nanofibers, hemp fibers, flax fibers, barium sulfate, silicon dioxide, silicon carbide, silicon nitride, aluminum oxide, aluminum nitride, titanium dioxide, titanium carbide, tin oxide, iron oxide, zinc oxide, magnesium oxide, magnesium hydroxide, zirconium oxide, cerium oxide, lithium oxide, silver oxide, a mixed metal oxide, silver, nickel, magnesium, zinc, montmorillonitey polyhedral oligomeric silsesquioxane, an aluminum alloy, a copper alloy, a gold alloy, an iron alloy, a nickel alloy, a platinum alloy, a silver alloy, a tantalum alloy, a tin alloy, a titanium alloy, and a zinc alloy.
 15. The material of claim 1, wherein the material comprises about 1.0-30.0 wt % nanofiller.
 16. The material of claim 15, wherein the material comprises about 15.0-30.0 wt % nanofiller.
 17. The material of claim 1, wherein the material comprises about 1.0-10.0 wt % nanofiller.
 18. The material of claim 17, wherein the material comprises about 1.0-5.0 wt % nanofiller.
 19. The material of claim 15, wherein the nanofiller comprises silver particles, and the material comprises about 15.0-30.0 wt % of the silver particles.
 20. The material of claim 1, wherein the nanofiller is modified by the inclusion of an organic functional group.
 21. The material of claim 20, wherein the organic functional group comprises: benzyl, hydroxyl, acetyl, phenyl, alkyoxy, alkyl, methyl, ethyl, propyl, substituted alkyls.
 22. The material of claim 1, wherein the nanofiller is modified by NaOH.
 23. The material of claim 1, wherein the nanofiller has an average size of about 10 nm-300 nm.
 24. The material of claim 23, wherein the nanofiller has an average size of about 10 nm-100 nm.
 25. The material of claim 1, wherein the material reduces the sound level by at least about 15 dB.
 26. The material of claim 25, wherein the material reduces the sound level by at least about 20 dB.
 27. The material of claim 26, wherein the material reduces the sound level by at least about 25 dB.
 28. The material of claim 27, wherein the material reduces the sound level by at least about 35 dB.
 29. The material of claim 1, wherein the material is in the form of a sheet or a layer having a thickness no greater than about 0.22 in.
 30. A sound barrier comprising the material of claim
 1. 31. A sound-emitting device comprising the sound barrier of claim
 30. 32. The material of claim 1, wherein the matrix comprises polyester. 